Problem: Multiply.
When a number is next to a variable, it means they are multiplied. So, $({5}{t^6})({7}{t^3})$ is the same as $({5})({t^6})({7})({t^3})$. Now we can rearrange the factors because multiplication is commutative (a fancy way of saying that the order in which we multiply things doesn't matter). ${(5)(7)}{(t^6)(t^3)}$ Then simplify, and we're done! ${35}{t^{9}}$